[DatePicker]: Value disappear on blur with dddd, D MMMM YYYY format

[MadinaNishanbaeva]

Prerequisites (optional)

Selected value disappear on blur

Please answer the following questions for yourself before submitting an issue.

• I am running the latest version
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed

Description (optional)

DatePicker lose value on blur
format: dddd, D MMMM YYYY
value: Thursday, 17 October 2024

Steps to Reproduce

    <DatePicker
      filter={(day: Dayjs) => {
        const today = new Date();

        return day.isAfter(today.setDate(today.getDate() - 1));
      }}
      mode="inline"
      disableClear={false}
      iconPosition="left"
      format={"dddd, D MMMM YYYY"}
      placeholder={t("form.placeholders.date")}
      {...lens.prop("date").toProps()}
    />

1. Choose date
2. Focus on input field, do not change date
3. Lose focus

Actual result

On blur value disappears

Expected result

On blur value is in the field

Environment

Please provide any relevant information about your setup. This is important in case the issue is not reproducible except for under certain conditions.

• UUI version: 5.9.0-beta.0
• Browser name: chrome
• Operating System: Windows

discussed with @siarhei-epam

[AlekseyManetov]

It seems that the 'dddd' token in the format string is not supported by Day.js - iamkun/dayjs#1802.
Additionally, it’s not listed among the available format tokens - https://day.js.org/docs/en/parse/string-format.

This behavior was never intended to work in UUI. However, Day.js can inconsistently parse its internal date object into a string with this format but fails to parse it back from the string into a Day.js object, resulting in an "Invalid date" error.

I believe that it may have partially worked previously due to a slightly different flow of focus/blur events. Perhaps the validation check was triggered at a different time or place, making it appear functional. However, I’m not confident that this didn’t cause undetected bugs or side effects.

I recommend changing this format to one that is fully supported by Day.js out of the box. I don’t think this issue can be fixed from the UUI side.